1. Field of the Invention
The present invention relates to a heat-release configuration for use as a countermeasure against heat of a semiconductor component having large heat generation, which is provided in a power source device. In particular, the present invention relates to a heat-release configuration having a clamp for supporting a heat-release plate in a printed board.
2. Description of the Related Art
Conventionally, in an electric component which is provided in a power source device, a heat-release plate made of aluminum, copper, iron or the like is mounted on a semiconductor component having especially large heat generation as a countermeasure against heat. Such a heat-release plate is mounted on a printed board by means of a screw, a rivet, manually bending a supporting clamp or the like.
Hereinafter, several methods of mounting a heat-release plate having a semiconductor component on a printed board will be described.
The first method is a method of mounting a heat-release plate on a solder surface of a printed board by soldering a semiconductor lead after screwing the heat release plate. The heat-release plate is firmly fixed to the printed board by this method. However, in an assembly process of a power source device, after mounting the heat-release plate on the printed board (a state in which the heat-release plate is only inserted into the printed board), the printed board is turned over by using a dedicated jig which fixes the heat-release plate for preventing the falling off of the heat-release plate, so as to turn the solder surface upward, and then the heat-release plate is soldered. In this case, it is necessary for a component attached to the heat-release plate to be manually soldered. For this reason, this first method is an inefficient method.
If a screw having a surface treatment to which solder adheres is used, the electrical connection between the heat-release plate and the printed board is improved. However, such a screw is expensive compared to a screw having a normal surface treatment, resulting in an increase in component costs.
In this case, the assembly process of the power source device is as follows. After an automatically insertable component is mounted on the printed board, a component which requires manual insertion is mounted on the printed board. Then, by dipping (in a solder bath), the component is soldered to the printed board. After that, the printed board is turned over so as to mount the heat-release plate, and then the manual soldering is performed.
The second method is a method of mounting a heat-release plate to a printed board by using a rivet. The heat-release plate is also firmly fixed to the printed board by this method. In this case, the workload of the operation of mounting the heat-release plate and the soldering operation in the assembly process of the power source device is less than that in the above-described soldering method.
However, the second method requires dedicated equipment (rivet machine), requires increased costs for maintaining consumable supplies, and may cause the operation failure of the dedicated equipment by the deterioration in the consumable supplies.
In this case, the assembly process of the power source device is as follows. At first, a component is automatically inserted into the printed board. After that, the heat-release plate is manually mounted on the printed board by using a rivet. Then, a component which requires manual insertion is mounted on the printed board. Then, by dipping (in a solder bath), the heat-release plate and the component are soldered to the printed board.
The third method is a method of mounting a heat-release plate to a printed board by manually bending a projection of the heat-release plate or a projection of a supporting clamp attached to the heat-release plate, which penetrates through the printed board. In this method, the projection which penetrates through the printed board and projects downwardly from the solder surface of the printed board is provided in each of both end portions of the heat-release plate. Or a supporting clamp or the like which penetrates through the printed board and projects downwardly from the solder surface of the printed board is mounted on the heat-release plate. The printed board and the heat-release plate are thereby firmly fixed, and the component can be soldered by dipping (in a solder bath).
However, in this third method, similar to the first method, it is necessary to mount the heat-release plate on the printed board by a dedicated jig (a state in which the heat-release plate is only inserted into the printed board), turn the solder surface of the printed board upward, and manually bend the heat-release plate or the supporting clamp. In addition, in this third method, the manual soldering operation of the heat-release plate is not necessary, and a workload is less than that in the above-described method of mounting the heat-release plate by soldering.
In this case, the assembly process of the power source device is as follows. At first, a component is automatically inserted into the printed board. After that, the heat-release plate or the supporting clamp is inserted into the printed board, the printed board is turned over, the heat-release plate or the supporting clamp is manually bent, and the heat-release plate is fixed to the printed board. Then, a component which requires the manual insertion is mounted on the printed board. By dipping (in a solder bath), the heat-release plate and the component are soldered to the printed board.
The fourth method is a method of mounting a heat-release plate to a printed board by forming the heat-release plate into a crank shape, or forming the supporting clamp provided in each of both ends of the heat-release plate into an L-shape such that the heat-release plate becomes self standable. In this method, the shape of the heat-release plate or the supporting clamp is devised such that the turning over operation of the printed board and the bending operation of the heat-release plate or the supporting clamp in the third method can be omitted.
However, due to the vibration and the like in the conveyor movement in the solder bath, the heat-release plate may be soldered to the printed board in a state in which the heat-release plate is inclined or the heat-release plate does not closely have contact with the printed board. In this case, the heat-release plate is pressed, causing pattern abrasion and a probability of solder cracks occurring by the vibration and impact is increased.
In this case, the assembly process of the power source device is as follows. At first, a component is automatically inserted into the printed board. After that, the heat-release plate is attached to the printed board. Moreover, a component which requires manual insertion is mounted. Then, by dipping (in a solder bath), the heat-release plate and the component are soldered to the printed board.
As described above, conventionally, the heat-release plate is assembled to the printed board of the power source device by the first to fourth methods or the like.
Japanese Utility Model No. 2571312 proposes a method of mounting an electric component on a heat-release plate by using a clip having a strong spring shape without using a screw when the electric component is mounted on the heat-release plate. By this method, a screw hole for mounting the electric component on the heat-release plate becomes unnecessary, a design freedom for disposing the electric component is improved, and the heat-release plate can be commonly used.
Hereinafter, the conventional example which mounts a heat-release plate on a printed board will be described by using a specific example of a heat-release plate assembly component.
FIGS. 8A-8D are views each illustrating a heat-release plate assembly component for use in a printed board of a power source device and a shape of a general heat-release plate and a shape of a supporting clamp. As illustrated in FIGS. 8A-8D, a semiconductor component (an element such as an FET and a diode) having a large heat generation volume is used in the power source device. As a countermeasure against the heat, the printed board 2 includes a heat-release plate 1 made of aluminum, copper, iron or the like. A semiconductor component 4 is screwed to the heat-release plate 1 by a screw 4c. Moreover, the heat-release plate 1 includes two or more supporting clamps 3.
In FIGS. 8A-8D, aluminum having a thickness of about 1-3 mm is introduced as the heat-release plate 1. The heat-release plate 1 has an L-shape to be self standable on the printed board 2 (it can be a U-shape, a Z-shape or the like). The heat-release plate has on one end portion thereof two small cylindrical convex portions 3a up and down and the other end portion thereof which is near the corner (near the corner of the L-shape) has two small cylindrical convex portions 3a up and down. The cylindrical convex portion 3a is used for mounting a supporting clamp as illustrated in FIGS. 9A-9C, and is formed by a half blanking process. These two convex portions 3a are inserted into two holes 3c (refer to FIG. 10A) formed in the supporting clamp 3, respectively. The supporting clamp 3 is thereby mounted on the heat-release plate 1. The convex portions 3a which project from the holes 3c of the supporting clamp 3 are crushed by a pressing process, the holes 3a of the supporting clamp 3 are shielded, and the supporting clamp 3 is firmly fixed to the heat-release plate 1.
The semiconductor component 4 is directly screwed to the semiconductor hole 4a by the screw 4c (pressing clamp or the like), and is mounted on the heat-release plate 1. The heat-release plate 1 to which the supporting clamp 3 and the semiconductor component 4 are assembled is mounted on the printed board 2.
FIGS. 10A, 10B are views each illustrating the shape of the supporting clamp 3 and the shape of a square hole provided in the printed board 2. The supporting clamp 3 is formed by a relatively soft thin material having a thickness of about t1=0.3 mm such as phosphor bronze and bronze, and has a solder plating surface. The supporting clamp 3 has a portion to be inserted into the printed board 2. This portion is divided into two having a fork shape, and the leading end portion of each divided portion has a tapered shape (tapered portion 3f). This portion includes a locking claw 3b which deforms inwardly when it is inserted into the square hole 5 of the printed board 2 and engages with the lower face of the printed board after the deformation.
The shape of the square hole 5 of the printed board 2 into which the insertion portion of the supporting clamp 3 is inserted is, with respect to the leading end portions of the insertion portion of the supporting clamp 3, A (the width of the locking claw 3b)>C (the length of the long side of the rectangular hole 5)>B (the width of the leading end potion of the insertion portion except the locking claw 3b). The rectangular hole 5 on the back face of the printed board 2 includes in the entire circumference thereof a pattern beaten-copper portion 2b. The entire circumference of the leading end portion of the insertion portion of the supporting claim 3 which projects from the back face of the printed board 2 is soldered to the pattern beaten-copper portion 2b of the printed board 2. Thereby, the supporting clamp 3 is fixed to the printed board 2.
FIGS. 11A-11 are views each illustrating change in the shape of the leading end portions of the supporting clamp 3 when the clamp 3 is mounted on the printed board 2. FIG. 11A illustrates a state in which the tapered portions 3f of the leading end portions of the insertion portion of the supporting clamp 3 are inserted until they have contact with the square hole 5 of the printed board 2, and does not illustrate changes in the shape of the leading end portions.
FIG. 11B illustrates a state in which the insertion portion of the supporting clamp 3 is further inserted into the printed board 2, so that the leading end portions of the insertion portion of the supporting clamp 3 are inserted into the square hole 5 of the printed board 2. The leading end portions of the insertion portion of the supporting clamp 3 deform by being pressed to both walls in the square hole 5 of the printed board 2, and the locking claws 3b stay in the square hole 5. The thickness of the supporting clamp 3 is about 0.3 mm, and the supporting clamp 3 is formed by a relatively soft material, so that the leading end portion of the insertion portion of the supporting clamp 3 easily deforms as described above. Therefore, the heat-release plate 1 can be easily and manually inserted without requiring increased strength for inserting the heat-release plate 1 to the printed board 2.
FIG. 11C illustrates a state in which the locking claws 3b of the leading end portions of the insertion portion of the supporting clamp 3 project from the undersurface (solder surface) of the printed board 2. The supporting clamp 3 does not have elasticity in the arrows D and D′ directions, so that the leading end portions do not return back to the original positions, respectively. Consequently, the width of the leading end portions becomes less than the width C of the square hole 5 of the printed board 2.
As described above, since the printed board 2 and the supporting clamp 3 are not physically locked, the heat-release plate 1 easily falls by lightly shaking the entire printed board 2 by hand. If the heat-release plate 1 falls by lightly shaking the printed board 2 by hand, the heat-release plate 1 easily inclines and falls in the conveyor movement in the solder bath. In order to ensure the fixed power of the heat-release plate 1 to the printed board 2, after the heat-release plate 1 is inserted into the printed board 2, it is necessary to bend with respect to the printed board 2 both or one of the leading end portions of the supporting clamp 3, which are divided into two (refer to FIGS. 8B, 8D).
FIGS. 12A-12D are views each illustrating a heat-release plate assembly component using a supporting clamp 13 different from the supporting clamp 3 illustrated in FIGS. 10A, 10B.
In FIGS. 12A-12D, the heat-release plate 11 is aluminum having a thickness of about 2-3 mm, and is a flat plate (is not curved into an L-shape or a U-shape). More specifically, the heat-release plate 1 has a configuration which can not stand by itself on the printed board 2.
The supporting clamp 13 has an L-shape in a cross section. The supporting clamp 13 is mounted on one end portion of the heat-release plate 11 by the screw 4c and the supporting clamp 13 is mounted on the other end portion of the heat-release plate 11 by the screw 4c. The semiconductor components 4 are mounted on the heat-release plate 11 by the screws 4c, respectively. The heat-release plate 11 has a U-shape as seen from the top in a state in which the supporting clamps 13 are mounted, and the heat-release plate 11 is standable on the printed board 2.
FIGS. 14A-14C are views each illustrating the supporting clamp 13 and the shape of the square hole 5 formed in the printed board 2. The supporting clamp 13 is made of solderable electrogalvanized steel having a thickness of about t2=0.8 mm, in order to ensure the strength of the supporting claim 13 and to be directly mounted on the supporting plate 11 by the screw 13a illustrated in FIG. 15A.
The leading end portion of the insertion portion of the supporting clamp 13 which projects from the back face of the printed board 2 includes on one side thereof a tapered shape (tapered portion 13c), and one locking claw 13b which engages with the back face (solder surface) of the printed board 2. The square hole 5 formed in the printed board 2 is formed such that the length C of the long side becomes longer than the length A of the locking claw 13b of the leading end portion of the insertion portion of the supporting clamp 13 by about 0.1-0.2 mm (C=A+0.1-0.2 mm).
The width (length of short side) of the square hole 5 of the printed board 2 is about 1.6 mm with respect to the thickness of the supporting clamp 13, t2=0.8 mm. The pattern beaten-copper portion 2b is formed in the entire circumference of the square hole 5. The entire circumference of the leading end portion of the supporting clamp 13 is soldered to the pattern beaten-copper portion 2b. 
The printed board 2 includes a hole 2c through which a lead 4b of the semiconductor component 4 penetrates. This hole 2c is formed such that the locking claw 13b of the supporting clamp 13 engages with the end of the square hole 54 of the printed board in a position offset by E+α.
FIGS. 15A, 15B are views each illustrating a screw having a spring washer and a flat washer for preventing looseness. The screw 13a includes a screw portion having a screw groove and an imperfect screw portion without having a screw groove. As illustrated in FIG. 15A, this imperfect screw portion includes the spring washer 6a and the flat washer 6b. 
Therefore, when mounting the supporting clamp 13 on the heat-release plate 11 by the screw 13a, the whole portion of the screw portion is not always threadably mounted on the heat-release plate 11, and a part of the screw portion is threadably mounted on the heat-release plate 11.
The measurement in which the screw portion is threadably mounted on the heat-release plate 11 is reduced if the thickness of the supporting clamp 13 and the heat-release plate 11 is reduced. For this reason, in order to reliably perform the screwing, it is necessary to use a material having a certain thickness for the supporting clamp 13. Consequently, although the strength of the supporting clamp 13 is increased, the elasticity of the supporting clamp is decreased, so that it becomes difficult to assemble the supporting clamp 13 to the printed board 2.
FIGS. 16A-16C are views each illustrating positional change between the leading end portion of the supporting claim 13 and the lead 4b of the semiconductor component 4 when mounting the supporting clamp 13 of FIGS. 14A-14C on the printed board 2.
Referring to FIG. 16A, the leading end portion of the supporting clamp 13 is inserted into the square hole 5 of the printed board 2 while inserting the lead 4b of the semiconductor component 4 into the offset hole 2c of the printed board 2. The bending force is thereby applied to the lead 4b of the semiconductor component 4.
FIG. 16B provides a view when the locking claw 13b of the leading end portion of the insertion portion of the supporting clamp 13 is inserted into the square hole 5 of the printed board 2. As illustrated in FIGS. 14A-14C, since the length A of the leading end portion of the insertion portion of the supporting clamp 13 including the locking claw 13b is set to be shorter than the length C of the square hole 5 of the printed board 2 by about 0.1-0.2 mm (refer to FIGS. 14A-14C), the leading end portion of the insertion portion of the supporting clamp 13 is inserted while the locking claw 13b has contact with the inner wall of the square hole 5. If the leading end portion of the insertion portion of the supporting clamp 13 is further inserted, the lead 4b of the semiconductor component 4 significantly curves, and the curving force to be applied to the lead 4b is increased.
FIG. 16C illustrates a state in which the locking claw 13b of the leading end portion of the insertion portion of the supporting clamp 13 projects from the back face (solder surface) of the printed board 2. If the locking claw 13b projects from the back face (solder face), the lead 4b of the semiconductor component 3 becomes free from the bending force, and the shape of the lead gets back to the original shape. By this lead 4b, the heat-release plate 11 to which the semiconductor component 4 is screwed and the supporting clamp 13 move in the arrow Y2 direction (the direction opposite to the arrow Y1), and the locking claw 13b of the leading end portion of the supporting clamp 13 engages with the back face of the printed board 2. Thereby, the heat-release plate 11 is fixed to the printed board 2.
With this fixing method, the heat-release plate 11 does not incline in the left direction of FIG. 16C. However, the leading end portion of the insertion portion of the supporting clamp 13 engages with the printed board 2 only on one side (right side in the figure), so that the inclination in the right direction is not completely controlled (refer to FIGS. 14A-14C).
The above-described mounting of the heat-release plate on the printed board in the power source device has a problem regarding workability when mounting the heat-release plate on the printed board, a problem regarding the installation of a dedicated fixing jig, a dedicated equipment and the like and the maintenance fee, a problem regarding the increase in a solder process, a problem regarding the inclination and the floating of the heat-release plate after soldering, a problem regarding the solder strength and the like.
When removing the heat-release plate fixed on the printed board by soldering from the printed board by the heat of the soldering iron, if the area of the soldered portion is large, the heat is taken by the heat-release plate. For this reason, it becomes difficult to remove the heat-release plate.